Edging rough round, that is a lens having both surfaces formed and processed according to prescription or pre-edged ophthalmic lenses, for example, adapting a rough round or pre-edge ophthalmic lens to fit a specific frame shape, is presently done by grinding-processing procedures.
Appropriate apparatus have been proposed which include a gripping device for the ophthalmic lens which grips the ophthalmic lens in such a manner that an edge to be processed is readily accessible. A turning unit slowly rotates the gripping device with the ophthalmic lens about an axis of rotation in such a manner that the entire edge of the ophthalmic lens comes consecutively in contact with a grinding tool. The tool is held in a supporting means and can be brought into contact with the edge area of the ophthalmic lens to be processed for the processing procedure. The grinding tool which, in the simplest form, is a lap which is also held on a shaft which a drive quickly turns. A control unit, which may be a copying control unit or an electronic control unit in which the form to be obtained is stored, brings the ophthalmic lens in contact with the grinding tool with respect to the angle of rotation of the gripping device of the respective ophthalmic lens in such a manner that an edged ophthalmic lens is produced.
Grinding devices on which the above described process is carried out are in use in a large number of optometrists' workshops as well as in central lens production facilities.
Disadvantages of the state of the art grinding devices are that the processing time is relatively long and it is not possible to work on both the edge and surface of the lens without re-chucking the grip and/or readjusting the respective ophthalmic lens, or without changing tools in order to carry out the various edge processing steps with the necessary precision required in a number of cases.
However, especially in central lens production facilities, it has recently become a practice to process the so-called prescription surface, that is, the production of both sides of a finished ophthalmic lens from a so-called blank and the edges of the ophthalmic lens, which previously the optometrist performed.
It is advantageous, particularly in the critical thickness, that is, the center thickness of the lens in a case of lenses having positive power and the thickness of the edge in the lenses having negative power, respectively, is to be minimized, to first pre-edge the delivered blank, for example, an ophthalmic lens finished only on one side, then finish the prescription surface and finally produce the exact contour of the edge including the bevel as well as carry out the de-burring step. This manner of proceeding means that it is necessary to re-grip the ophthalmic lens several times. However, each re-gripping step harbors the danger of errors.